Compared with conventional oil and gas resources, production of unconventional shale oil or tight gas faces more challenges, because low-permeability reservoir rock generally results in low productivity and low recovery rates. Currently, the two technologies most frequently used in shale oil and gas recovery are horizontal drilling and hydraulic fracturing (also called “fracking” or “fracing” herein). Horizontal drilling and hydraulic fracturing have made possible the successful development of shale oil and gas and tight oil and gas resources by effectively reducing oil and gas flow resistance and increasing flow rates by increasing the contact area between the wellbore and the reservoir, but also have serious shortcomings. First, formation damage due to water imbibing and fluid trapping hinders the production of oil and gas; this problem is particularly severe in low-permeability reservoirs due to the elevated capillary pressure. Second, hydraulic fracturing operations use large amounts of water, proppants, and chemical additives. There has been rising concern about the environmental impact of conventional fracking technology, and in particular about groundwater and surface water contamination and inadequate treatment of the wastewater generated by fracking, leading to restrictions on fracking in the interest of public safety. It is therefore a top priority to develop alternative and effective well and reservoir stimulation technologies that significantly reduce the use of chemicals, conserve water, avoid structural damage to groundwater-bearing strata, and prevent groundwater contamination.
In all unconventional oil and gas reservoir development, some form of well and reservoir stimulation is required. The technique most commonly used is hydraulic fracturing, an established technique in the United States. Fracturing can provide hydraulic conductivity throughout the reservoir and reach deep into the reservoir for improved reserve recovery. Rising public concerns over water usage and groundwater contamination make it necessary to consider alternatives or supplementary techniques that will mitigate public and environmental concerns and improve the oil and gas recovery from unconventional resources with minimal damage to overburdened groundwater-bearing strata.
In addition, one of the costliest and most time-consuming operations in conventional oil and gas drilling occurs when an operator desires to change operating modes. Many existing systems and methods utilize a drill head with a single function and/or single mode, or with multiple functions or modes that cannot be switched remotely. The use of such drill heads requires the operator to withdraw the drill string from the reservoir, switch or adjust the drill head, and reinsert the drill string back into the reservoir. This withdrawal and reinsertion of the drill string is known as “tripping,” because it involves a “round trip” of the drill string. Depending on local conditions, tripping can take multiple hours to complete, greatly increasing the amounts of time and money needed to drill wells. There is thus a need for drilling devices, methods, and systems which may be switched remotely from aboveground, eliminating the need for arduous tripping of the drill string.